Respiratory mask system with vent assembly

ABSTRACT

A vent assembly for use with a respiratory mask of the type used in CPAP treatment includes a porous disk portion that is attached to a biasing member such that the disk portion is maintained in a substantially sealed position against a main vent to minimize airflow through at least one side vent of the vent assembly. Debris build-up on the disk portion can cause the biasing member to deflect to provide an additional path for airflow through the at least one side vent. In another embodiment, the vent assembly can also include an anti-asphyxia feature to provide an airflow path from the environment to the user. An oxygen diverter valve may be disposed between the breathing apparatus flow generator and an oxygen injection port.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/019,590, filed Sep. 6, 2013, now allowed, which is a continuation ofU.S. application Ser. No. 13/405,503, filed on Feb. 27, 2012, now U.S.Pat. No. 8,528,562, which is a continuation of U.S. application Ser. No.12/048,603, filed Mar. 14, 2008, now U.S. Pat. No. 8,146,596, which is adivisional of U.S. application Ser. No. 10/870,549, filed Jun. 18, 2004,now U.S. Pat. No. 7,559,326, which claims the benefit of U.S.Provisional Application No. 60/479,188, filed Jun. 18, 2003, eachincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to the field of treatment for breathingdisorders. More specifically, the present invention relates to the ventof a respiratory mask for ventilatory treatment or assistance.

The present invention also relates to an oxygen diverter valve used insystems where air or another breathable gas is mixed with oxygen. Thevalve may be used in conjunction with the vent. The valve has beendeveloped primarily for use between a gas delivery apparatus fordelivery of breathable gas and an oxygen port. One goal is that thatwhen airflow is stopped the valve closes and prevents oxygen to flowupstream into the flow generator.

The valve is also suitable for use in other gas delivery systems, suchas those used in assisted respiration and Non-Invasive Positive PressureVentilation (NIPPV).

2. Background Information

The application of Continuous Positive Airway Pressure (CPAP) via a maskis a common ameliorative treatment for sleep disordered breathing (SDB),including obstructive sleep apnea (OSA). In CPAP treatment for OSA, airor other breathable gas is supplied to the entrance of a patient'sairways at a pressure elevated above atmospheric pressure, typically inthe range 3-20 cm H₂O as measured in the patient interface. It is alsoknown for the level of treatment pressure to vary during a period oftreatment in accordance with patient need, that form of CPAP being knownas automatically adjusting CPAP treatment.

Typically, the patient interface for CPAP treatment can include a nasalmask. The nasal mask is generally defined by a mask shell that forms aninner cavity defined by its interior surface, a mask cushion and theuser's face, and a gas inlet. A swivel elbow may be coupled to the gasinlet, or the gas inlet may be attached directly to a conduit thatsupplies the air or breathable gas. Alternatively, a nose-mouth mask,full-face mask, nasal prongs or nasal pillows may be used. One exampleof a nasal mask is described in U.S. patent application Ser. No.09/570,907, which is incorporated herein by reference in its entirety.

An apparatus including a mask should be quiet and comfortable toencourage patient compliance with therapy; however, exhausting exhaledair from a vent into the atmosphere may create noise. Because CPAPtreatments are normally administered while the patient is sleeping,minimization of such noise is desirable for both the comfort of thepatient and any bed partner. Accordingly, a need has developed in theart to overcome the deficiencies of prior art devices that mayundesirably make noise.

The inventor has discovered that a vent with fine holes or a ventcovered with a finely meshed porous material similar to Gore-Tex® may beused to produce a respiratory mask having low vent noise. However, theinventor identified two potential problems encountered by the use of thevent including fine holes or the vent covered with finely meshedmaterial. The first problem may occur if the vents of the mask becomeblocked or clogged with debris. The blocked vents reduce airflow throughthe vents, which could cause a high level of CO₂ to accumulate in themask and thereby create a safety concern to the user. The second problemmay occur if the vents are manufactured with the intent of obtainingrepeatable pressure flow characteristics, because it is difficult toconsistently duplicate the vents of the mask at a precision required toget repeatable pressure flow characteristics.

Based upon the above, the inventor has identified a need for a vent thatis quiet, comfortable, and constructed of a material that overcomes theproblems of potential high CO₂ levels and permits consistentpressure-flow characteristics to be achieved.

SUMMARY OF THE INVENTION

Devices consistent with the principles of the present invention, asembodied and broadly described herein, overcome one or more of thedifficulties indicated above and others by providing a device thatutilizes a porous material having fine holes as vents to produce arespiratory mask having very low noise. Moreover, these features may beobtained while preventing the risk of high CO₂ levels and obtainingconsistent pressure flow characteristics.

In one embodiment of the present invention, a vent assembly for arespiratory mask includes a main vent portion configured to permit gasto flow via a primary flow path through a mask shell to the environmentwhen the respiratory mask is in use during a first predeterminedcondition of the vent assembly. A porous disk portion is configured tosubstantially seal against the main vent portion to provide the primaryflow path through the main vent portion and the disk portion during thefirst predetermined condition of the vent assembly. A secondary ventportion is configured to provide a secondary flow path when apredetermined second condition of the vent assembly and flow pressurecauses a predetermined deflection of the disk portion.

In another embodiment of the present invention, a vent assembly for arespiratory mask includes a main vent portion formed in a mask shell andconfigured to permit gas to flow via a primary flow path through themask shell to the environment when the respiratory mask is in use duringa first predetermined condition of the vent assembly. A flap portionincludes a porous section and a flap insert wherein the flap portion isconfigured to substantially seal against the main vent portion toprovide the primary flow path through the main vent portion and theporous section of the flap portion during the first predeterminedcondition of the vent assembly. The flap portion is further configuredto develop a gap between the mask shell and the flap portion when apredetermined second condition of the vent assembly and flow pressurecauses a predetermined deflection of the flap to provide a secondaryflow path from the mask shell around the flap portion to theenvironment.

In yet another embodiment of the present invention, a vent assembly fora respiratory mask includes a main vent portion configured to permit gasto flow via a primary flow path through a mask shell to the environmentwhen the respiratory mask is in use during a first predeterminedcondition of the vent assembly. A secondary vent portion is configuredto provide a secondary flow path during a predetermined second conditionof the vent assembly and flow pressure, wherein the predetermined secondcondition occurs when the main vent portion is blocked by apredetermined amount of debris.

The oxygen diverter valve is typically used in an airflow to whichoxygen is added. The valve is typically placed between the flowgenerator and the oxygen injection point.

The valve preferably includes two cavities separated by a flap. Thefirst (upstream) cavity is connected to the air supply. The second(downstream) cavity connects to the oxygen injection port. Thedownstream cavity is also open to the atmosphere via several closablevents. The flap which separates both cavities includes a mounting rim, ahinged flap section and a sealing section.

At rest, the flap is typically in a closed position, thereby preventingthe gas from flowing upstream from the oxygen injection cavity into theair supply cavity. When the flap is in closed position the gas in theoxygen injection cavity can vent into the atmosphere.

When the relative air pressure in the air supply cavity exceeds acertain level the flap is forced open allowing the air to flowdownstream from the air supply cavity into the oxygen injection cavity.The flap closes the vents to the atmosphere when open.

The operating threshold can be altered to suit particular applications.For example, a valve suitable for use in adult ventilatory assisttherapy has an operating threshold of less than 2 cm H₂O.

Preferably, the housing includes two housing parts that are releasablyengageable with one another. In an embodiment, the housing parts engageby way of clip style fittings. Preferably, the housing includes a gasinlet in the form of a female conical connector adapted to frictionallyengage a flexible conduit in fluid communication with the gas deliveryapparatus and a gas outlet in the form of a male conical connectoradapted to engage an oxygen injection point or a flexible or rigidconduit in fluid communication with the mask.

Desirably also, one of the gas inlets or outlets includes asnap-engageable and detachable swivel portion adapted to engage the maskor flexible conduit. In a preferred embodiment, the inlet and outlet arerespectively provided on one of the two housing parts.

In an embodiment, the housing includes several vents spaced about theperiphery of the oxygen injection cavity.

The mounting ring of the flap preferably includes a rim which fitssnugly into a receiving cavity in the housing. The mounting ring canhave a square, round or tapered cross section.

In one preferred form, the flap is substantially round. In other forms,the flap can be full or part elliptical, rectangular or any other shape.

The housing is preferably manufactured from plastics material, forexample polycarbonate (Bayer Makrolon 2458). The flap assembly ispreferably manufactured from a flexible elastomeric material such as asilicone rubber (Dow Corning Silastic 94-595-HC).

In a further embodiment, the housing is of unitary construction.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention arefurther described in the detailed description which follows, withreference to the drawings, and by way of non-limiting exemplaryembodiments of the present invention, wherein like reference numeralsrepresent similar parts of the present invention throughout the severalviews and wherein:

FIG. 1A illustrates an exploded view of a vent assembly of a respiratorymask in accordance with an embodiment of the present invention;

FIG. 1B illustrates a vent assembly of a respiratory mask in accordancewith an embodiment of the present invention;

FIG. 2 illustrates the flow characteristics of a main vent and side ventin accordance with an embodiment of the present invention;

FIG. 3 illustrates a visual indicator of a disk condition in accordancewith an embodiment of the present invention;

FIG. 4A illustrates an open, extra air path of an anti-asphyxia valve inaccordance with an embodiment of the present invention;

FIG. 4B illustrates a closed, extra air path of an anti-asphyxia valvein accordance with an embodiment of the present invention;

FIG. 5A illustrates an alternate anti-asphyxia valve during inhalationin accordance with an embodiment of the present invention;

FIG. 5B illustrates an alternate anti-asphyxia valve with partial debrisbuild up during exhalation in accordance with an embodiment of thepresent invention;

FIG. 5C illustrates an alternate anti-asphyxia valve with substantiallyno debris build up during exhalation in accordance with an embodiment ofthe present invention;

FIG. 6A illustrates a respiratory mask having a vent assembly inaccordance with another embodiment of the present invention;

FIG. 6B illustrates an exploded view of the vent assembly of FIG. 6A;

FIG. 7A illustrates a vent assembly in accordance with anotherembodiment of the present invention;

FIG. 7B illustrates the vent assembly of FIG. 7A with debris blockage;

FIG. 8A illustrates a vent assembly in accordance with yet anotherembodiment of the present invention;

FIG. 8B illustrates the vent assembly of FIG. 8A with debris blockage;

FIG. 9A illustrates a vent assembly in accordance with yet anotherembodiment of the present invention;

FIG. 9B illustrates a valve housing, a holder portion and a springportion of the vent assembly of FIG. 9A;

FIG. 10 is a general schematic drawing of a system comprising a flowgenerator being connected to a valve and mask via tubing in which themask is connected to a patient, according to another embodiment of thepresent invention;

FIG. 11 is a side view/cutaway view of a valve of the present invention;

FIG. 12 is a perspective view of an embodiment of a flap according tothe present invention;

FIG. 13 is a cross sectional view of FIG. 11 in which the flow generatoris not operating;

FIG. 14 is a cross sectional view of the valve of FIG. 11 in which theflow generator is operating and generating a pressure differential abovethe operating threshold;

FIG. 15 is a cross sectional view of a further embodiment of the presentinvention wherein the valve has a unitary housing;

FIG. 16 is a cross sectional view of a yet further embodiment of thepresent invention wherein the valve includes a swivel conduit connector;

FIG. 17 is a cross sectional view of a yet further embodiment of thepresent invention wherein the valve includes an oxygen injection point;

FIG. 18 is a cross sectional view of an embodiment of a flap with adifferent rim;

FIG. 19 is a cross sectional view of another embodiment of a flap with adifferent rim;

FIG. 20 is a cross sectional view of yet another embodiment of a flapwith a different rim;

FIG. 21 is a cross sectional view of another embodiment of a flap with adifferent toroid;

FIG. 21.1 is a cross sectional view of another embodiment of a flap withyet another toroid;

FIG. 22 is a cross sectional view of yet another embodiment of a flapwith a different toroid;

FIG. 23 is a perspective view of an alternative embodiment of thepresent invention wherein the valve is attached to a mask; and

FIG. 24 is a perspective view of another embodiment of the presentinvention wherein the valve is integral with a mask.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1A illustrates an exploded view of a vent assembly 100 of arespiratory mask frame 110 in accordance with a first embodiment of thepresent invention. The mask frame 110 includes at least one side vent108, a main vent 106, a bellows portion 104, and a disk portion 102attached to an end of the bellows portion 104. Bellows portion 104 maybe, for example, constructed from a silicone material or other suitableflexible material known in the art. The bellows portion 104 can have afirst bellows section 104A and a second bellows section 104B constructedand arranged to provide a biasing force. Bellows portion 104 may also besubstituted by a biasing member such as a spring that is assembled tothe mask frame 110. Disk portion 102 may be, for example, a porous platehaving multiple, finely-spaced holes and/or a piece of finely meshedfabric.

As illustrated in FIG. 1A, the disk portion 102 may be attached to thetop of bellows portion 104 such that a biasing force produced by thebellows portion 104 maintains the disk portion 102 in a sealed positionagainst an inside of the main vent 106 opening.

FIG. 1B illustrates the bellows portion 104 arranged within the maskhousing 110 such that the disk portion 102 is flush with the main vent106. A bellows stop 111 (illustrated in phantom) within the mask frame110 can be arranged to support the bellows portion 104 or biasing memberwhen the bellows portion 104 or biasing member and the disk portion 102are assembled within the mask frame 110. Portions of the first bellowssection 104A and the second bellows section 104B are visible through theside vent 108.

In use, a flow generator provides a constant positive pressure to theinterior of the mask. Airflow caused by the positive pressure and/or airexhaled by the user is vented to the environment via the vent assembly100. Preferably, the biasing force of the bellows portion 104 is greaterthan or equal to the force applied to the disk portion 102 by airflowpressure when the disk is in a clean condition and exposed to flowpressure during use. The sealed positioning of the disk portion 102against the main vent 106 minimizes airflow through the side vent 108.

As an example of the function of the force applied to the disk portion102 by flow pressure, the following is provided. A projected area of thedisk portion 102 can be determined based upon an area of the diskportion 102 excluding the finely-spaced holes, passages or pores. Forexample, a disk portion 102 which is 50% porous and has an area of 10mm² would have a projected area of 5 mm². The projected area is exposedto the flow pressure. The force applied by the flow pressure to the diskportion 102 can be calculated by multiplying the flow pressure with theprojected area of the disk portion 102. When the disk portion 102 is ina clean condition, i.e., there is little or no debris build-up on thedisk portion 102, the total projected area of the disk portion 102 thatis exposed to the flow pressure is low. Accordingly, the force appliedby the flow pressure to the disk portion 102 does not exceed the forceapplied in the opposite direction by the bellows portion 104 to the diskportion 102, and the bellows portion 104 is not significantlycompressed. As such, air flows primarily through the holes or passagesin the disk portion 102. Airflow is minimized through the side vent 108because the disk portion 102 is not substantially displaced by the flowpressure and minimizes exposure of the side vent 108 to the primaryairflow path.

However, when the disk portion 102 is in an unclean condition, i.e.,when there is a build-up of debris on the disk portion 102, the totalprojected area of the disk portion 102 exposed to the flow pressure isincreased by the debris build-up that blocks air flow through the holesor passages in the disk portion 102 and increases the total projectedarea. A proportional relationship can exist between the debris build-upon the disk portion 102 and the total projected area exposed to flowpressure, i.e., as the debris build-up increases, the total projectedarea exposed to the flow pressure increases. Accordingly, the forceeffectively applied to the disk portion 102 by the flow pressureincreases.

The increase of force applied to the disk portion 102 can displace thedisk portion 102 in the direction of flow pressure and can cause thebellows portion 104 to compress, providing a path for the airflow tobypass the disk portion 102 by permitting secondary airflow through sidevent 108. The amount of secondary airflow through side vent 108 can beproportional to the amount of debris build-up on the disk portion 102(depending at least upon the shape of the side vent 108 and the springforce provided by the bellows portion 104). The extra force applied tothe disk portion 102 can be directly related to the increased projectedarea created by the debris build-up, i.e., as the blocked area of thedisk portion 102 increases, the force applied to the bellows portion 104also increases. Preferably, the vent assembly 100 is configured andarranged such that, regardless of the debris build-up and associateddisplacement of the disk portion 102, total combined airflow through themain vent 106 and the side vent 108 remains substantially constant.

FIG. 2 is a graph that illustrates the flow characteristics of the mainvent 106 and side vent 108 of the respiratory mask in accordance with anembodiment of the present invention. In FIG. 2, the flow rate ismeasured in units of liters per minute (L/min) along the y-axis. Anindex to indicate the build-up of debris on disk portion 102 is measuredin units of millimeters squared along the x-axis. The total flow of airmay be a constant value as indicated by line 200. The assembly may alsooperate at various pressures such that the line 200 would indicatevariable flow rates at various flow pressures. When the disk portion ismaintained in a clean condition, i.e., the debris build-up index is low,the flow rate through the main vent 106 is higher. The flowcharacteristics of the main vent 106 are shown as line 204. However, asthe debris build-up index increases, the flow rate through the side vent108 increases. The flow characteristics of the side vent 108 are shownas line 206.

The flow characteristics of the side vent 108 may be altered, forexample, by changing the stiffness or biasing force of the bellowsportion 104, by changing the diameter or area of the disk portion 102,by selecting material of various flow impedance characteristics for thedisk portion 102, or by changing the opening size, number of and/orshape of the side vent 108.

The flow characteristics of the main vent 106 may be altered, forexample, by changing the diameter or area of the disk portion 102, byselecting material of various flow impedance characteristics for thedisk portion 102, by changing the opening size, number of and/or shapeof the side vent 108, or by changing the stiffness or biasing force ofthe bellows portion 104.

As an option to assist the user in ascertaining the amount of debrisbuild-up on the disk portion 102, the vent assembly may include amechanism to sense and/or indicate the condition of the disk portion102. FIG. 3 illustrates a visual indicator 300 of a disk condition inaccordance with an embodiment of the present invention. In FIG. 3, anindicator 304 that is attached to the disk portion 102 may be used todisplay, via a window 302, the level of debris build-up. Window 302 ispreferably transparent.

The indicator 300 may perform sensing, for example, by anelectro-mechanical contact or optical sensor. The sensing portion of themechanism could preferably produce a pulse or continuous stream ofenergy that may be detected by a receiving device. Each of the receivedsignals may be logged to create a database containing information thatmay be used to analyze various aspects of the vent assembly. Forexample, an event may be sensed by the mechanism and logged as an entrythat the user may observe upon waking the next morning. In thealternative, an event may be sensed and an auditory or visual signalprovided to the user immediately to indicate the occurrence of aparticular condition or event in the vent assembly. The mechanism usedto provide the auditory or visual signal may be, for example, attachedto the disk portion 102 to indicate the amount of debris build-up and/orwhether the disk portion 102 needs to be replaced.

The information about the vent condition provided by a sensing mechanismor other suitable device can have several uses. For example, a warningmay be activated based on the information whereby a clogged conditioncan be logged. An auditory signal (arousing noise or synthetic voicewarning) and/or visual signal can be given to the user. A visual signalcan be discretely given via a readout on a display screen and noticed bythe user when, for example, the user addresses the flow generator uponwaking at the end of a normal sleep period. The visual signal can alsobe given by way of a light of sufficient brightness and/or intensitycalculated to awaken the user.

The vent condition information can be converted into a signal which canbe transmitted to a distant location. Preferably, the signal istransmitted via a public communication network such as the publictelephone system or the Internet. Additionally, the vent conditioninformation can be sent to a supplier or other appropriate receiver andused to automatically order a replacement vent, which can be dispatchedautomatically to the user.

The side vent 108 can be configured such that flow through the side vent108 produces an audible sound, for example a whistling sound, to alertthe user to debris build-up. Additionally, the vent assembly 100 canincorporate a microphone to monitor sounds produced by the vent assembly100, in particular, sounds generated by air flow through the side vent108. The sounds can be logged as an event, or they can be amplified towake the user. The sounds can also be recorded or used to trigger analarm or suitable device to alert the user to debris build-up, asexplained above with respect to the vent condition information.Additionally, the vent assembly 100 can be configured such that movementof the disk portion 102 with respect to the vent assembly 100 causes anappropriate signal to be generated, such as a sound, visual indicationor electronic signal.

In the event that there is stoppage of airflow to the respiratory mask,it is possible that a continuous positive flow of breathable air is notprovided for the user to breathe. Flow stoppage can occur, for example,during a power failure in which the flow generator arranged to provideairflow does not operate. A vent assembly that allows flow out of themask to the environment but does not allow flow into the mask from theenvironment could potentially cause the user to asphyxiate during flowstoppage. Accordingly, the vent assembly may be configured and arrangedto include an anti-asphyxia feature, such as that illustrated in thevent assembly in FIGS. 4A and 4B. The anti-asphyxia feature can allowairflow into the mask from the environment during flow stoppage when theuser inhales.

It is contemplated that an anti-asphyxia feature can be obtained bychanging the orientation of the vent assembly 100 with respect to themask frame 110. For example, the vent assembly 100 can be arranged suchthat the disk portion 102 faces outward away from the mask interior andthe bellows portion 104 faces inward toward the mask interior. A ventassembly 100 with such an orientation can be provided in addition to anexisting vent assembly 100 with a typical orientation to provide ananti-asphyxia feature to the typically oriented vent assembly 100.

FIG. 4A shows an additional flow path 402 provided in the mask frame 110to allow flow from the environment into the mask interior to prevent theuser from asphyxiating during flow stoppage. The side vent 108 is notvisible in this view, and the bellows portion 404 and the bellows stop111 within the mask frame 110 are illustrated in phantom. When the userof the respiratory mask breathes in during flow stoppage, the bellowsportion 404 stretches towards the mask interior (to the right asillustrated in FIG. 4A) and allows the disk portion 102 to move towardsthe mask interior. The movement of the disk portion 102 opens the flowpath 402 and allows air to flow through flow path 402. Flow path 402 isconfigured such that slight displacement of disk portion 102 results ina relatively large opening in flow path 402. When a constant positivepressure exists in the mask interior, the bellows portion 404 is notstretched towards the mask interior, and the disk portion 102 can closethe additional flow path 402. The closed flow path 402 is illustrated inFIG. 4B, and the disk portion 102 is visible through the flow path 402.

FIGS. 5A-5C illustrate an alternate anti-asphyxia valve that may beincluded in the vent assembly in accordance with an embodiment of thepresent invention. In FIGS. 5A-5C, disk portion 102 is made of aflexible material, for example, a membrane material, to permit the diskportion 102 to flex with respect to the bellows portion 104.Additionally, disk portion 102 may be connected to the vent assembly atthe center of bellows portion 104 by a fastener 504 to permit maximumflexibility of the disk portion 102. FIGS. 5A-5C also show two sidevents 108.

FIG. 5A illustrates the anti-asphyxia valve during flow stoppage whenthe user of the respiratory mask frame 110 inhales. Flow in thedirection of arrow 506 flexes disk portion 102 towards the inside of themask frame 110. Air entering the mask frame 110 via main vent 106 andside vents 108 results in airflow in the direction of arrow 506, evenwhen the disk portion 102 may have substantial debris blockage.

FIG. 5B illustrates the anti-asphyxia valve when the disk portion 102has partial debris blockage during use. Airflow in the direction ofarrow 502 caused by constant positive pressure in the respiratory maskframe 110 and/or exhalation by the user can push disk portion 102against bellows portion 104, compressing the bellows portion 104 (i.e.,the primary flow path via the disk portion 102 is partially blockedresulting in secondary air flow via the side vents 108) such that airflows from the mask frame 110 via the main vent 106 and side vents 108.Airflow via the main vent 106 and the side vents 108 depends at leastupon the amount of debris blockage of the disk portion 102. Asillustrated, the bellows portion 104 is partially compressed, indicatingpartial debris blockage of the disk portion 102.

FIG. 5C illustrates the anti-asphyxia valve when the disk portion 102 issubstantially clean and free of debris blockage during use. Airflow inthe direction of arrow 502 slightly pushes disk portion 102 againstbellows portion 104. However, because the disk portion 102 issubstantially clean, the bellows portion 104 is not substantiallycompressed by the primary air flow. Accordingly, air flows from the maskframe 110 via the primary flow path through the main vent 106. Air flowvia the secondary flow path through side vents 108 is substantiallyminimized.

FIG. 6A illustrates a vent assembly of a respiratory mask in accordancewith another embodiment of the present invention. The mask housing 612includes an orifice 610 (see FIG. 6B) and a flap portion 602 that isheld in position over the orifice 610 by a retainer mechanism 604.Typically, the flap portion 602 and the retainer mechanism 604 of thevent assembly are located on the exterior of the mask housing 612 suchthat they do not interfere with the operation of other aspects of themask, such as the coupling of the mask to a flow generator or operationof any mask ports or any user interfaces such as facial cushions.

The orifice 610 and vent assembly are also located such that theoperation of the vent assembly is not readily subject to interference bythe user or the user's environment, especially during sleep. Anexemplary location of the orifice 610 and vent assembly in the maskhousing 612 is at a position to the right or left of the user's nose ona side of the mask. Alternatively, multiple vents can be provided. Twovents can be used, one located on each side of the mask to the right andto the left of the user's nose.

FIG. 6B illustrates an exploded view of the vent assembly of FIG. 6A.Flap portion 602 may be made of a flexible material, and an interiorsection may be covered with a porous mesh material 606. The meshmaterial 606 of the flap portion 602 is configured to cover the orifice610 having a predetermined diameter. The flap portion 602 is held inposition over the orifice 610 via an insert portion 608 configured tofit retainer mechanism 604.

In FIG. 6B, orifice 610 functions as a main vent portion to regulate theairflow of the respiratory mask such that the direction of primaryairflow is through the mesh material 606 of the disk portion 602.However, as debris build-up accumulates on mesh material 606, a gap candevelop between the mask housing 612 and the flap portion 602. The sizeof the gap, created by movement of the flap portion 602 away from maskhousing 612, can be proportional to the force applied by flow pressureto the flap portion 602. The force can be proportional to the increasedtotal projected area caused by debris build-up on the mesh material 606.The gap between the mask housing 612 and the flap portion 602 canprovide a secondary airflow path bypassing the flap portion 602.

The return force or biasing force of flap portion 602 to return to itsposition on mask housing 612 can depend upon the flexibility of thematerial of the flap portion 602 and the shape and/or thickness of theinsert portion 608. For example, flap portion 602 may be made from asilicone material, and mask housing 612 may be made from a polycarbonateor other similar material. The selection of silicone for the flapportion 602 and polycarbonate for the mask housing 612 would create ahigh static attraction between the flap portion 602 and the mask housing612. The high static attraction between the flap portion 602 and themask housing 612 may be used to augment or serve as the return force orbiasing force of the flap portion 602. Retainer mechanism 604 canincorporate a hinge mechanism and/or a spring to vary the return forceof the flap portion 602.

The flap portion 602 can be made as a disposable item. The relativelysimple construction can allow for a low cost of manufacture.Accordingly, the flap portion 602 can be disposed of and replaced as analternative to being cleaned. Additionally, the flap portion 602 can beinstalled easily into the retainer mechanism 604, without complicateddisassembly of the vent assembly or mask. The user can readily removeand dispose of a clogged flap portion 602 and install a clean flapportion 602.

The following exemplary dimensions in Table 1 can be used to provide aflow rate of 20 L/min during a positive internal mask pressure of 2 cmH₂O when using the embodiment illustrated in FIGS. 6A and 6B:

TABLE 1 Orifice Diameter  3 mm Mesh Material Diameter 10 mm MeshMaterial Nylon Flap Portion Diameter 20 mm Insert Portion Width  9 mmInsert Portion Thickness 0.12 mm   Flap/Insert Portion MaterialPolyesterIt is contemplated that the above dimensions can be reduced if multiplevent assemblies are provided. For example, if two vent assemblies areprovided, the above dimensions can be halved for each vent assembly toeffectively achieve the same flow rate.

The embodiment of a vent assembly illustrated in FIGS. 6A and 6B canincorporate an anti-asphyxia feature in the form of an auxiliary orifice(not shown) with a corresponding auxiliary flap and retainer mechanism(not shown) configured to allow airflow from the environment into themask during flow stoppage when the user inhales. For example, theauxiliary flap can be arranged on the inside of the mask surface to sealthe auxiliary orifice such that inhalation in the absence of normalairflow causes the flap to deflect inwards and allow air from theenvironment through the auxiliary orifice into the mask for the user tobreathe. The auxiliary flap can be non-porous to prevent flowtherethrough and to prevent debris buildup on the auxiliary flap. Theauxiliary flap can be configured and arranged such that pressurerequired to cause inward deflection of the auxiliary flap is low.Accordingly, the user does not experience difficulty in breathing duringflow stoppage. It is contemplated that the auxiliary orifice and flapcan provide an anti-asphyxia feature to a mask incorporating otherembodiments of a vent assembly (for example, the vent assembly 100illustrated in FIGS. 1A and 1B).

An anti-asphyxia feature can be incorporated into the flap portion 602,insert portion 608, retainer mechanism 604 and orifice 610 by using aflap portion 602 with an outer diameter equal to the inner diameter ofthe orifice 610 so that a pressure seal can develop between the flapportion 602 and the orifice 610, while allowing the flap portion 602 todeflect inwards during flow stoppage when the user inhales. Preferably,the insert portion 608 and/or the retainer mechanism 604 are constructedsuch that deflection away from the mask interior maintains apredetermined flow characteristic, while deflection towards the maskinterior allows the user to breathe easily. For example, the insertportion 608 can be biased such that inward deflection occurs more easilythan outward deflection. Additionally, a hinge can be incorporated toallow inward deflection under a low force, while outward deflectionrequires a higher force commensurate with desired flow characteristics.Alternatively, the flap portion 602 and the retainer mechanism 604 canbe arranged on the inside of the mask such that outward deflection ofthe flap portion 602 away from the mask interior through the orifice 610requires a higher force than inward deflection. Accordingly, the usercan breathe easily during flow stoppage.

FIG. 7A is a cross-sectional view of a vent assembly 700 of arespiratory mask in accordance with another embodiment of the presentinvention. The vent assembly 700 includes a disk portion 702, a bellowsor spring biasing portion 704 and a main vent 706 arranged in a maskhousing or valve housing 710. A plurality of side vents 708 are formedin the valve housing 710. Preferably the valve housing 710 iscylindrical. The valve housing 710 can further be arranged to provide adisk stop 722 to retain the disk portion 702 within the valve housing710 against a force created by the spring portion 704 applied to thedisk portion 702.

A spring force from the biasing portion 704 can maintain the diskportion 702 in a sealed position against the main vent 706 portion suchthat the side vents 708 are not substantially exposed to a primary flowpath such that a majority of flow passes through the disk portion 702.The biasing force exerted by the biasing portion 704 upon the diskportion 702 is greater than or equal to the force exerted by flowpressure upon a projected area of the disk portion 702 when the diskportion 702 is in a clean condition. As shown in FIG. 7B, debris 720 canaccumulate on the disk portion 702. As debris 720 accumulates, the forceexerted by flow pressure increases, causing the biasing portion 704 tocompress in the direction of flow and causing the disk portion 702 tomove with respect to the valve housing 710 away from disk stop 722.

When the biasing portion 704 is compressed by the force exerted by flowpressure, the disk portion 702 can be positioned to allow flow through aplurality of side vents 708. Side vents 708 can have a wedge shape (asshown in FIGS. 1A and 1B) or other suitable shape, depending upondesired secondary flow characteristics of the vent assembly 700.Alternatively, additional vents can be arranged further along the pathof movement of the disk portion 702 beyond side vents 708 such that theyare exposed to airflow at various levels of displacement as the diskportion 702 is displaced by flow pressure. Biasing portion 704 can be aspring. Because it is not necessary to provide a flow path through thebiasing portion 704, the biasing portion 704 can be a bellowsconstructed using a suitable material such as silicone, which preventsairflow therethrough. It is contemplated that the bellows can beconstructed from a porous material or can be permeated with holes toallow airflow, and can incorporate a predetermined airflow impedance.

FIG. 8A is a cross-sectional view of a vent assembly 800 of arespiratory mask in accordance with yet another embodiment of thepresent invention. The vent assembly 800 includes a disk portion 802, aspring or bellows biasing portion 804, and a main vent 806 arranged in avalve housing 810. Unlike the embodiment shown in FIGS. 7A and 7B, thevent assembly 800 does not include side vents, although side vents canbe used to augment the embodiment shown in FIG. 8A. The valve housing ispreferably cylindrical and is arranged to provide a disk stop 822 toretain the disk portion 802 within the valve housing 810.

The disk portion 802 can move with respect to the valve housing 810,against the biasing pressure of the biasing portion 804, along thedirection of flow through the main vent 806. The valve housing 810 isfurther arranged such that at least a portion of the inner walls 814 ofthe valve housing 810 form a draft angle 824 between the direction ofmovement of the disk portion 802 and the inner walls 814 of the valvehousing 810.

As illustrated in FIG. 8B, build-up of debris 820 causes pressure fromprimary flow to displace the disk portion 802 in the direction of flow.Due to the draft angle 824 of at least a portion of the inner walls 814,a gap 826 is developed between the inner walls 814 and a peripheral ofthe disk portion 802. Accordingly, secondary airflow can bypass the diskportion 802 via the gap 826. Because the secondary flow takes asecondary pathway including the biasing portion 804, the biasing portion804 preferably can transmit the secondary flow. The biasing portion 804can be a spring. In embodiments where biasing portion 804 is a bellows,the bellows is constructed with suitable porous or permeated material toaccommodate the secondary flow. The flow impedance of the biasingportion 804 also can be used to vary the secondary flow characteristicsof the vent assembly 800.

The draft angle 824 illustrated in FIGS. 8A and 8B is approximately 5-15degrees, and preferably 10 degrees. The angle preferably remainssubstantially constant along the extent of the entire inner wall 814.Accordingly, the gap 826 increases proportionately in relation to thedisplacement of the disk 802. However, it is contemplated that the draftangle 824 can be greater than or less than 5-15 degrees, and the draftangle 824 can vary along the extent of the inner wall 814 (i.e., theinner wall 814 can be curved), depending upon the desired secondary flowcharacteristics and desired development of the gap 826 throughout thedisplacement of the disk portion 802.

Additionally, only a circumferential portion of the inner wall 814 alongthe circumference of the valve housing 810 can be shaped to include thedraft angle 824, whereas the remaining portions of the inner wall 814along the circumference of the valve housing 810 can remainperpendicular to the displacement of the disk portion 802. Portions ofthe inner wall 814 perpendicular to the displacement of the disk portion802 can act as a guide to stabilize the disk portion 802 duringdisplacement.

FIG. 9A illustrates a vent assembly 900 of a respiratory mask inaccordance with yet another embodiment of the present invention. Thevent assembly 900 includes a valve housing 910, a spring biasing portion904, a holder portion 912, and a disk portion 902. The valve housing 910is composed of a first portion 930 and a second portion 932. The firstportion 930 and the second portion 932 are illustrated as hollowcylinders arranged and connected to each other coaxially, the secondportion 932 having a diameter greater than the diameter of the firstportion 930. The first portion 930 forms a recess 934 (see FIG. 9B). Thesecond portion 932 forms a main vent 906 shaped to allow airflow to passwithin the inner circumference of second portion 932, through aplurality of passages 928 at the interface between the first portion 930and the second portion 932 (see FIG. 9B), and along the outercircumference of the first portion 930. The diameters of the firstportion 930 and the second portion 932 are chosen to correspond todiameters of respective parts (base portion 936 and receiving portion938) of the holder portion 912.

The holder portion 912 includes a base portion 936 and a receivingportion 938. The base portion 936 of the holder portion 912 slidablyengages the recess 934 of the first portion 930. The receiving portion938 of the holder portion 912 is sized to slidably engage at least aportion of the inner circumference of the main vent 906 of the valvehousing 910.

The biasing portion 904 engages the base portion 936 of the holderportion 912 and engages the first portion 930 of the valve housing 910.The biasing portion 904 provides a spring force between the valvehousing 910 and the holder portion 912, allowing the holder portion 912to slide along the axis of the valve housing 910. The holder portion 912accordingly can move with respect to the valve housing 910.

The porous disk portion 902 is attached to the receiving portion 938 ofthe holder portion 912. The disk portion 902 sealably engages at least aportion of the inner circumference of the second portion 932 of thevalve housing 910. Preferably, a majority of the outer circumference ofthe disk portion 902 sealably engages at least a portion of the innercircumference of the main vent 906.

The disk portion 902 can be fixedly secured to the receiving portion 938of the holder portion 912 using glue or other suitable adhesive. Thedisk portion 902 also can be mounted to the receiving portion 938 via acentral fastener (not shown) passing through a disk hole 916 in the diskportion 902 and anchored to a holder hole 918 in the holder portion 912.The disk portion 902 and the holder portion 912 are shaped to receivethe central fastener. The central fastener can mount the disk portion902 to the receiving portion 938 without the use of glue, allowing allor portions of the disk portion 902 to separate from the receivingportion 938 under specific flow conditions.

Separation of all or portions of the disk portion 902 from the receivingportion 938 can provide an anti-asphyxia feature similar to theanti-asphyxia feature of the embodiment illustrated in FIGS. 5A-5C. Toprovide the anti-asphyxia feature in the vent assembly 900, the porousdisk portion 902 is preferably made of a flexible material which canflex away from the receiving portion 938 to break a seal with the innercircumference of the main vent 906, depending upon flow conditions anddebris build up in use. Alternatively or additionally, the anti-asphyxiafeature can be accomplished by using a flexible central fastener (notshown) for the disk portion 902. A flexible central fastener canflexibly extend and allow the disk portion 902 to separate from thereceiving portion 938 and the inner circumference of the main vent 906,even if the disk portion 902 is not flexible. A spring also can be usedin conjunction with the central fastener to allow displacement of thedisk portion 902, depending upon flow conditions and debris build up inuse.

FIG. 9B illustrates the valve housing 910 in more detail. The secondportion 932 of the valve housing 910 includes at least one side vent908. As illustrated, the side vent 908 is in the form of a groove havinga tapering depth along an axial extent of the second portion 932. Inparticular, the depth of the side vent 908, i.e., the radial distancefrom the axis of the second portion 932 to the side vent 908, increasesas the side vent 908 extends axially towards the first portion 930 ofthe valve housing 910. The side vent 908 is illustrated as occupying theentire axial extent of the second portion 932. Accordingly, the diskportion 902 does not sealably engage the side vent 908 of the secondportion 932, but rather, the disk portion 902 sealably engages theremaining circumference of the second portion 932 not occupied by theside vent 908.

FIG. 9B illustrates a plurality of passages 928 formed in the valvehousing 910 at the interface between the first portion 930 and thesecond portion 932. In use, air can flow through a primary flow pathincluding the porous disk portion 902 and the plurality of passages 928in the valve housing 910. When the disk portion 902 is substantiallyfree of debris blockage, the biasing portion 904 can maintain the diskportion 902 in an upper position. In the upper position, a crosssectional area of the side vent 908 is minimized. Accordingly, secondaryflow through the side vent 908 is minimized.

As the disk portion 902 becomes blocked with debris, the flow pressurecauses the disk portion 902 to move towards a lower position. As thedisk portion 902 moves towards the lower position, the cross sectionalarea of the side vent 908 increases. The increase in the cross sectionalarea of the side vent 908 allows an increase in secondary flow throughthe side vent 908, compensating for the decrease in primary flow throughthe disk portion 902 caused by debris blockage.

It is contemplated that, in alternate embodiments, the side vent 908does not occupy the entire axial extent of the second portion 932. Forexample, the side vent 908 can occupy a lower portion of the secondportion 932, i.e., a part of the second portion 932 nearer to the firstportion 930. Accordingly, the disk portion 902 would sealably engage theentire circumference of the second portion 932 when the holder portion912 is in the upper position. It is also contemplated that a pluralityof side vents 908 can be used. Additionally, the side vent 908 can bearranged such that the circumferential width of the groove formed by theside vent 908 varies. The circumferential width of the side vent 908 canvary in addition to or as an alternative to varying the radial depth, toprovide a varying cross sectional area of the side vent 908 throughoutthe range of movement of the holder portion 912 between the upper andlower positions.

Varying the circumferential width of the side vent 908 can allow for aconsistently minimized radial depth of the side vent 908 while stillproviding a varying cross sectional flow area of the side vent 908throughout the range of movement of the holder portion 912. For example,the side vent 908 can have a wedge shape similar to the shape of theside vent 108 illustrated in FIGS. 1A and 1B. A minimized radial depthof the side vent 908 can allow for a minimized radial thickness of thesecond portion 932 of the valve housing 910, compared to an increasedthickness of the second portion 932 to accommodate the varying radialdepth of the side vent 908. A reduction in the radial thickness of thesecond portion 932 of the valve housing 910 can minimize the overallsize of the valve housing 910.

While not illustrated in detail in FIGS. 4A-9B, it is contemplated thatthe illustrated embodiments of a vent assembly can incorporate a visualindicator and/or sensing mechanism. An anti-asphyxia valve can beincorporated, in the form of an additional flow path provided in themask and/or valve housing, and/or in the form of a flexible material inthe disk portion. Additionally the valve assembly can be formed in anon-cylindrical shape.

FIGS. 10-24 illustrate an oxygen diverter valve which can be usedindependently of, instead of, or in conjunction with the valve describedabove. The oxygen diverter valve can be used for any air or oxygendelivery system in which there is some type of flow generator connectedto a tube or airflow conduit with oxygen injection which is thereaftersecured to a face mask. The transmitted gas can be any type ofbreathable or therapeutic gas.

The general schematic of this is shown in FIG. 10 where flow generator 3with a flexible airflow conduit which is secured to an embodiment of avalve 1 of the present invention. The oxygen injection point 2 islocated downstream of the valve 1 and is thereafter connected to a nasalmask 4 of a patient 5. The mask shown is just one example of numeroustypes of patient interface.

The location of the valve 1 shown in FIG. 10 is just one example ofnumerous possible locations. The valve 1 should preferably be placedbetween flow generator 3 (or the equipment that is to be shielded fromthe oxygen) and the oxygen injection point 2.

The flow generator 3 produces a flow of breathable gas, typically air,and can be an electric blower, a controlled bottled gas system, aventilator, or any other type of device that delivers breathable,therapeutic or anaesthetic gas.

The valve 1 shown in FIG. 11 is comprised of two housing parts 6 and 7which may be locked together by way of respective male and female clipfittings 8 and 9. The housing part 6 includes an inlet in the form of afemale conical portion 10. The housing part 7 includes an outlet in theform of male conical portion 11. The portions 10 and 11 allow push-onassembly and frictional engagement with the gas supply conduit 12 andthe oxygen supply conduit 12 a, respectively. The housing part 7includes one or more peripherally arranged vents 12 a.

In the embodiment shown in FIGS. 11 to 14, a preferably flexible flap 13of generally round cross-section is formed from a silicone rubber andhas a central orifice.

As shown in FIG. 12 the flap 13 includes a first portion in the form ofouter rim 14. The outer rim 14 is clamped or otherwise attached ormounted into a corresponding recess in the housing part 7. Cast-on lugs17 a and 17 b are used when positioning the flap 13.

The flap 13 includes a second portion in the form of a flexible hingedsilicone membrane 15. The hinge shape allows the flap 13 to flex betweenthe closed and open positions, as shown in FIG. 13 and FIG. 14respectively. A third portion 16 resists crinkling or bending of themembrane. Third portion 16 includes a stiff toroid part which forms theactual seal.

The flap 13 is preferably manufactured by moulding of a single siliconerubber component in the shape shown in FIG. 12 (closed position). In thepreferred embodiment the flap 13 is nominally 0.15 mm thick. Thethickness of the flap is adjusted to suit its application and, inparticular, the operating threshold pressure. If the flap is too flimsyit may not close at the correct pressure and if it is too stiff the flapwill not open at the correct pressure.

As shown in FIG. 13, when the difference in the gas pressure between airinlet cavity 18 and the atmosphere is below a predetermined operatingthreshold of, for example 2 cm H₂O, the flap 13 is in a relaxed (closed)state. The toroid 16 is resting on the valve core 20 blocking the oxygenrich gas flow from the oxygen injection cavity 19 from entering the airinlet cavity 18. The gas flows from the oxygen injection cavity 19through the vents 12 to the atmosphere.

When the gas supply from the flow generator 3 commences or resumes andthe difference in the gas pressure between the air inlet cavity 18 andthe atmosphere builds up to equal or above 2 cm H₂O, the flap 13 movesto an “open” position whereby vents 12 are closed as shown in FIG. 14.The flap 13 is kept open as long as the pressure in the air inlet cavity18 remains above the predetermined operating threshold. In the openposition all the gas supplied from the flow generator 3 passes throughthe orifice of the flap 13 into the air injection cavity 19, mixes withthe oxygen supplied and is delivered to the patient via the facemask.

The inherent resilience of the flap 13 re-closes the valve and re-opensvents 12 when the pressure difference between the air inlet cavity 18and atmosphere falls below the predetermined operating threshold.

Testing of a prototype of the valve 1 shown in FIGS. 10 to 14 wasconducted with a flow generator connected to the inlet cylindricalportion 10 via an airflow conduit. An oxygen supply and a mask wereconnected to the valve 1 at the outlet cylindrical portion 11 simulatingnormal use. With this arrangement the valve had an operating thresholdof less than 2 cm H₂O pressure difference.

FIG. 15 illustrates an embodiment of the valve 1 having a unitaryhousing 21.

FIG. 16 illustrates another embodiment of the valve 1 with a snap onswivel connector 22 that engages over resilient fingers 23. Thisembodiment obviates the need for a separate swivel connector elsewherein the, gas supply circuit.

In another embodiment (not shown) the swivel connection 23 is used inconjunction with the unitary housing 21.

FIG. 17 shows an embodiment of the valve 1 with an oxygen injectionpoint 2 cast into the downstream housing 7.

In another embodiment (not shown) the oxygen injection point 2 is castinto the unitary housing. The oxygen injection point can also be used inconjunction with a snap-on swivel connector.

FIG. 18 shows an embodiment of the flap 13 which includes an externalrim 24 of stepped cross section which assists in locating the flap 13 inthe housing(s). The rim 24 is received within a corresponding recess24.1 (see, e.g., FIG. 15) in the housing to facilitate locating andmounting the flap 13 in the housing.

FIG. 19 shows another embodiment of the flap 13 having an external rim25 of rectangular cross section.

FIG. 20 shows yet another embodiment of the flap 13 having asubstantially cylindrical formation 26 between the flaps and the rim 27.The cylindrical formation 26 and the rim 27 facilitates locating theflap correctly within the housing.

FIG. 21 shows an embodiment of the flap 13 with a circular shaped crosssection of the toroid 28. FIG. 21.1 shows a flap 13 having a seal in theform of a full or part ellipse 33.

FIG. 22 shows an embodiment of the flap 13 with a triangular shapedcross section of the toroid 29.

FIG. 23 illustrates an embodiment of the valve 1 in which the valve isattached to a face mask 30 with an oxygen injection point 2.

FIG. 24 illustrates a further embodiment of the valve 1 incorporatedinto a mask 31 with an oxygen injection point 2. In this embodiment, thevalve 1 is integrally formed with the mask shell 32 thereby obviatingthe push-on connection between the mask 31 and the valve 1.

The valve according to the present invention can be used for any type ofair delivery system, it is preferably used in CPAP applications for thetreatment of OSA or Non-Invasive Positive Pressure Ventilation (NIPPV).

Preferred embodiments of the valve of the present invention have theadvantage of being able to operate independent of orientation. That is,although the valve has to be connected in the right direction betweenthe flow generator and the mask, it can be inverted, held sideways, etc.which often occurs during the time when the patient sleeps.

Another advantage of the valve of the present invention is it has onlyone moving or flexing part providing consistent operation. Further, thevalve can be disassembled cleaned and reassembled very easily at home orat a hospital or clinic due to it having fewer parts. The valve of thepresent invention is also very quiet in operation.

Although the invention has been described with reference to specificexamples, it will be appreciated by those skilled in the art that theinvention may be embodied in many other forms. In particular, a valve ofthe present invention may be constructed of components which havedimensions, configurations and mechanical properties (including themechanical properties of the flap assembly) that vary from those of thedisclosed embodiments. Such valves can have operating thresholdsdifferent from valve embodiments which achieved a closure at 2 cm H₂O.The actual dimensions, configurations and mechanical properties will bechosen to achieve a valve having performance characteristic includingoperating threshold that will meet the specific needs of the chosenapplication.

The foregoing description of the embodiments of the present inventionprovides illustration and description, but is not intended to beexhaustive or to limit the invention to the precise form disclosed.Modifications and variations are possible consistent with the aboveteachings or may be acquired from practice of the invention withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A respiratory mask system for treatment of apatient having a breathing disorder, the mask system comprising: a maskhaving a shell having an air inlet to receive breathable gas in apressure range of 3-20 cm H₂O, and a mask cushion to contact thepatient's face; headgear to maintain the mask in position on thepatient's head in use; and a vent assembly radially surrounding the airinlet to allow gas to exhaust from the mask, the vent assembly having amain vent portion and a secondary vent portion, wherein, in use of thesystem: a total combined airflow through the main vent portion and thesecondary vent portion remains substantially constant over time, eventhough a ratio of airflow through the main vent portion compared to thesecondary vent portion is variable over time, and the airflow throughthe main vent portion is substantially equal to the airflow through thesecondary vent portion at a first point in time, and the airflow thoughthe secondary vent portion is greater than the airflow through the mainvent portion at a second point in time, later than the first point intime.
 2. A respiratory mask system for treatment of a patient having abreathing disorder according to claim 1, wherein airflow through themain vent portion is reduced when force acting on the main vent portiondue to air pressure is increased.
 3. A respiratory mask system fortreatment of a patient having a breathing disorder according to claim 1,further comprising an elbow extending from the air inlet and adapted toconnect to an air delivery conduit coupled to a flow generator.
 4. Arespiratory mask system for treatment of a patient having a breathingdisorder according to claim 3, wherein the vent assembly surrounds theelbow.
 5. A respiratory mask system for treatment of a patient having abreathing disorder according to claim 1, wherein the main vent portionis associated with a deflectable member configured to deflect with flowpressure, and wherein the flow through the main vent portion decreasesas the deflectable member progressively deflects, such that a percentageof the total combined airflow due to airflow through the secondary ventportion increases.
 6. A respiratory mask system for treatment of apatient having a breathing disorder, the mask system comprising: a maskhaving a shell having an air inlet to receive breathable gas in apressure range of 3-20 cm H₂O, and a mask cushion to contact thepatient's face; headgear to maintain the mask in position on thepatient's head in use; and a vent assembly to allow gas to exhaust fromthe mask, the vent assembly having a main vent portion and a secondaryvent portion, wherein, in use of the system: a total combined airflowthrough the main vent portion and the secondary vent portion remainssubstantially constant over time, even though a ratio of airflow throughthe main vent portion compared to the secondary vent portion is variableover time, the airflow through the main vent portion is substantiallyequal to an airflow through the secondary vent portion at a first pointin time, and the airflow though the secondary vent portion is greaterthan the airflow through the main vent portion at a second point intime, later than the first point in time, and the main vent portion isassociated with a deflectable member configured to deflect with flowpressure, wherein the flow through the main vent portion decreases asthe deflectable member progressively deflects, such that a percentage ofthe total combined airflow due to airflow through the secondary ventportion increases.
 7. A respiratory mask system for treatment of apatient having a breathing disorder according to claim 6, whereinairflow through the main vent portion is reduced when force acting onthe main vent portion due to air pressure is increased.
 8. A respiratorymask system for treatment of a patient having a breathing disorderaccording to claim 6, further comprising an elbow extending from the airinlet and adapted to connect to an air delivery conduit coupled to aflow generator.
 9. A respiratory mask system for treatment of a patienthaving a breathing disorder according to claim 8, wherein the ventassembly surrounds the elbow.
 10. A respiratory mask system fortreatment of a patient having a breathing disorder according to claim 6,further comprising a flexible airflow conduit having a proximal endconnected to the frame and configured to deliver the breathable gas tothe air inlet of the frame, and a distal end supporting and in fluidcommunication with the vent assembly.